This invention relates to the barrel of a gun mounted on, for example, a tank. More particularly, the invention relates to a gun barrel provided with a heat pipe for dispersing the heat which is generated locally in the barrel by sunlight or when the gun is fired.
A tank, shown schematically shown in FIG. 1, includes a main body 1 and a gun barrel 2. The upper side of the barrel 2 has a large increase in temperature as when exposed to sunlight, but its lower side, which is not exposed to sunlight, has only a small rise in temperature. The resulting difference in the amount of thermal expansion between its upper and lower sides causes the barrel 2 having a large length l to flex downwardly at its free end by an amount .delta. indicated in FIG. 2. This flexure depends largely on the weather conditions, and has a significant bearing on the hit probability.
Each time the gun is fired, the barrel receives an impact from the gas which is produced by the accompanying explosion, and heat is generated by the mechanical friction between a fired shell and the surface of the bore of the barrel. The barrel is, therefore, heated to a high temperature, shortening its life. The thermal expansion of the barrel enlarges its bore diameter and thereby forms a clearance between the shell and the inner surface of the barrel. The combustion gas leaks through the clearance and wears the inner surface of the barrel. The enlarged bore diameter in turn causes a change in the contact resistance between the shell and the barrel, and this change adversely affects the initial speed of the shell and its hit probability. This is particularly the case when the gun is fired continuously. The heating is concentrated on the base end of the barrel and its upper side to which heat is transmitted by convection. It is thus necessary to provide an arrangement which promotes a uniform distribution of the heat throughout the barrel and its dissipation therefrom.
It is generally believed that the amount of heat which is transmitted to the barrel is a function of the flow speed and density of the gas in the barrel and the temperature of its flame, and that about 5 to 8% of the heat generated by the combustion of the explosive is transferred to the barrel. Only a very short time is, however, available for such heat transfer, and thus only the inner surface of the barrel is heated each time the gun is fired. If the gun is fired continuously, the inner surface of the barrel is heated to a higher temperature each time, and the whole barrel is eventually overheated until firing cannot be continued.